Generally, in an image display device provided with a fluorescent screen, excitation light is irradiated from one surface side of the fluorescent screen, and fluorescence (fluorescent image) is observed from the other surface side of the fluorescent screen.
In a phosphor layer, fluorescence emitted from a phosphor exits from both surfaces (front and rear surfaces) of the phosphor layer, and an image is formed by the fluorescence that exits from the front surface of the phosphor layer. In this case, the fluorescence that exits from the rear surface of the phosphor layer does not contribute to image formation, and hence ight utilization efficiency of fluorescence is reduced.
Patent Literature 1 discloses a fluorescent screen which can improve the utilization efficiency of fluorescence. The fluorescent screen includes a visible light reflecting layer which transmits excitation light and which reflects visible light, and a phosphor layer formed on the visible light reflecting layer.
The excitation light is irradiated from the side of the visible light reflecting layer of the fluorescent screen, and the phosphor in the phosphor layer is excited by the excitation light transmitted through the visible light reflecting layer. The fluorescence emitted from the phosphor and propagating toward the surface of the phosphor layer, whose surface is located on the side of the visible light reflecting layer, is reflected by the visible light reflecting layer in the direction of the phosphor layer. In this case, in addition to the fluorescence that is emitted from the phosphor and that exits from the surface of the phosphor layer, whose surface is located on the side opposite to the visible light reflecting layer, the fluorescence reflected by the visible light reflecting layer also contributes to the image formation, and hence light utilization efficiency is improved.
Patent Literature 2 discloses another fluorescent screen. This fluorescent screen includes a phosphor layer, and a reflecting layer which is provided to face the phosphor layer and which reflects excitation light and visible light. The reflecting layer has an opening to restrict the region of the phosphor layer, onto which region the excitation light is irradiated.
The excitation light passes through the opening of the reflecting layer, so as to be irradiated onto the phosphor layer. In the phosphor layer, fluorescence is emitted from the phosphor in which the excitation light is absorbed. The emitted fluorescence propagates toward the surface of the phosphor layer, whose surface is located on the side of the reflecting layer, and also the emitted fluorescence propagates toward the surface of the phosphor layer, whose surface is located on the side opposite to the reflecting layer. The fluorescence that propagates toward the surface of the phosphor layer, whose surface is located on the side of the reflecting layer, is reflected by the reflecting layer in the direction of the phosphor layer. Also, in this case, similarly to the fluorescent screen described in Patent Literature 1, light utilization efficiency of fluorescence can be improved.
In the fluorescent screens described in Patent Literatures 1 and 2 described above, a dielectric multilayer film can be used as the visible light reflecting layer and the reflecting layer.